This invention relates to urethane polymer compositions, particularly moisture-reactive hot-melt urethane polymer compositions useful as adhesives, to a method for making such compositions, and to a method for bonding substrates with such compositions.
Some moisture-reactive hot-melt polymer compositions are useful as reactive hot-melt adhesives. Some desirable properties of such adhesives are high green strength, high ultimate strength, and long open time. Green strength is the bond strength prior to completion of the reaction with moisture; ultimate strength is the adhesive strength after the reaction with moisture is essentially complete; and open time is the period of time after the hot-melt adhesive is applied to one or more substrates, during which subsequent substrates may be contacted with the adhesive, without loss of ultimate strength.
U.S. Pat. No. 5,021,507 discloses the modification of polyurethane reactive hot melts with acrylic copolymers of specific molecular weight, in which the polymer contains no monomer with active hydrogen. U.S. Pat. No. 5,827,926 discloses the use of crystalline acrylic polymers containing no active hydrogens.
The approaches taken in the past that have achieved good green strength have also had undesirably short open times. The problem faced by the inventor is the provision of a moisture-reactive hot-melt adhesive composition that achieves a desirably long open time while maintaining usefully high green strength. Surprisingly, the inventor found that incorporation of certain acrylic polymers having tertiary-alkyl amide functionality provided the desired balance of properties.